Re: [libvirt] [PATCH] qemu: configurable VNC port boundaries for domains
On Tue, May 22, 2012 at 09:09:55AM -0600, Eric Blake wrote:
On 05/22/2012 09:00 AM, Dave Allan wrote:
> On Tue, May 22, 2012 at 04:10:03PM +0200, Martin Kletzander wrote:
>> The defines QEMU_VNC_PORT_MIN and QEMU_VNC_PORT_MAX were used to find
>> free port when starting domains. As this was hardcoded to the same
>> ports as default VNC servers, there were races with these other
>> programs. This patch includes the possibility to change the default
>> starting port as well as the maximum port in qemu config file.
>
> Hi Martin,
>
> Two design comments:
>
> 1) https://bugzilla.redhat.com/show_bug.cgi?id=782814 requests that
> the default port be changed to avoid conflicts, which seems reasonable
> to me.
If we choose better defaults for new installations, we still need to
worry about preserving existing ranges when upgrading old installations.
This may need some coordination with the spec file doing some %post
magic to add in vnc_port_min with a value other than 5900 to qemu.conf
on new installations, but leaving it unspecified when doing an upgrade.
That's a good point, we certainly don't want to break things on
upgrade. At least one case that would is where people have opened the
old range in a firewall, and now instead of ports, say, 5900-n, now
people will be getting some other range.
> 2) I agree with the config option since most applications on
the
> system will want the system defaults. However, IMO in this case an
> application writer should be given the option in the XML to override
> the system default.
Agreed - I think we need both solutions - qemu.conf to specify the
default range, and per-domain XML to specify an override (does the XML
need to specify a range, or just a single port?).
I think a range, like the config option.
>> +++ b/src/qemu/qemu_command.h
>> @@ -37,6 +37,9 @@
>> # define QEMU_VIRTIO_SERIAL_PREFIX "virtio-serial"
>> # define QEMU_FSDEV_HOST_PREFIX "fsdev-"
>>
>> +/* These are only defaults, they can be changed now in qemu.conf and
>> + * explicitely specified port is checked against these two (makes
s/explicitely/explicitly/
>>
>> + p = virConfGetValue (conf, "vnc_port_min");
>> + CHECK_TYPE ("vnc_port_min", VIR_CONF_LONG);
>> + if (p) {
>> + if (p->l < QEMU_VNC_PORT_MIN) {
>> + /* if the port is too low, we can't get the display name
>> + * tell to vnc (usually subtract 5900, e.g. localhost:1
>> + * for port 5901) */
>> + qemuReportError(VIR_ERR_INTERNAL_ERROR,
>> + _("%s: vnc_port_min: port must be greater than
or equal to %d"),
>> + filename, QEMU_VNC_PORT_MIN);
You ought to mention this restriction in qemu.conf.
>> + p = virConfGetValue (conf, "vnc_port_max");
>> + CHECK_TYPE ("vnc_port_max", VIR_CONF_LONG);
>> + if (p) {
>> + if (p->l > QEMU_VNC_PORT_MAX ||
>> + p->l <= driver->vncPortMin) {
Off-by-one. You want to allow min==max for specifying a range of
exactly 1 port, useful if you are only running one guest and want to
guarantee its port. You need p->l < driver->vncPortMin, not p->l <=
driver->vncPortMin.
>> +++ b/src/qemu/qemu_conf.h
>> @@ -89,6 +89,8 @@ struct qemud_driver {
>> unsigned int vncSASL : 1;
>> char *vncTLSx509certdir;
>> char *vncListen;
>> + long vncPortMin;
>> + long vncPortMax;
long? We know it's only 16 bits; short would do, int might be easier to
work with, but long is overkill.
--
Eric Blake eblake(a)redhat.com +1-919-301-3266
Libvirt virtualization library http://libvirt.org